Polymers, and novel compositions and films therefrom

ABSTRACT

A novel propylene copolymer is disclosed. Also disclosed is a novel composition comprising about 85 to about 99 weight percent of a polymeric ethylenic containing component having a density no greater than 0.94 g/cc, and about 1 to about 15 weight percent of a novel propylene copolymer comprising from about 60 to about 80 weight percent propylene, based on the copolymer, and from about 20 to about 40 weight percent olefin comonomer units, the propylene copolymer having a viscosity of about 1 to about 2,000 mPa•s at 190° C. and a needle penetration of greater than about 150 to about 300 dmm. Also disclosed are films produced from the composition, both blown and cast, and both monolayer and multilayer. Also disclosed are processes for stretch wrapping and forming blown film.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. Section 119(e) toUnited States Provisional Application Ser. No. 60/058,769, filed Sep.12, 1997. The present application is related to co-pending U.S.application Ser. Nos. 09/104,726, 09/104,726, 09/145,452, and09/145,451.

FIELD OF THE INVENTION

The present invention relates to novel polymers and use thereof incompositions having particular utility in the production of film. Moreparticularly, the present invention relates to novel propylenecopolymers and compositions comprising a blend of an ethylene polymerand the novel propylene polymers having particular utility in theproduction of film, especially stretch wrap cling film.

BACKGROUND OF THE INVENTION

Blown stretch wrap film generally has higher tensile strength than castfilm. Linear low density polyethylene ("LLDPE") is much more useful thanlow density polyethylene ("LDPE") as the film-forming component of blownstretch wrap films. However, a cling additive must be blended with LLDPEsince LLDPE film does not exhibit a high level of cling when stretchedin the typical usage to about 200 percent elongation. The film made fromthe composition of the present invention generally also has an unwindingnoise not greater than the unwinding noise of the neat ethylenicpolymer. This is important in light of the OSHA noise workplacerestrictions.

June 1992 U.S. Research Disclosure 33875 discloses that a polyolefinhaving a Brookfield Thermosel Viscosity of about 6,000 mPa•s at 190° C.,and a needle penetration hardness of about 35 dmm and a polyolefinhaving a Brookfield Thermosel viscosity of 2300 mPa•s at 190° C. and aneedle penetration hardness of 20 dmm are useful in cast and blown LLDPEand LDPE film. The applicant has found that blown polyethylene basedstretch cling films containing these polyolefins have little or no peelcling strength at 200 percent elongation. The applicant has previouslydisclosed a very low viscosity partially crystalline propylene-ethylenecling additive for EVA, LDPE, and LLDPE stretch film composition. Thedisclosed propylene-ethylene cling additive comprises a partiallycrystalline propylene-ethylene copolymer having 10 to 40 weight percentethylene units, within the viscosity range of 1 to 2,000 mPa•s at 190°C. The known propylene-ethylene copolymer cling additive has a needlepenetration hardness less than about 150 dmm at 23° C. The filmcomposition disclosed therein is more useful for film blowing than arefilm compositions made with the above higher viscosity polyolefins.However, the previously disclosed blown film has a peel cling strengththat is lower than cast films containing the above higher viscositypolyolefin cling additives.

In light of the above, it would be desirable to have apolyethylene-based film having the combination of excellent blown filmproperties as well as relatively high peel cling strength.

SUMMARY OF THE INVENTION

The present invention relates to novel propylene copolymers describedhereinafter and to a composition of matter which comprises about 85 toabout 99 weight percent based on the composition of an ethyleniccomponent selected from the group consisting of low densitypolyethylene, linear low density polyethylene, ethylene vinyl acetatecopolymer and mixtures thereof; and about 1 to about 15 weight percentbased on the composition of a novel propylene copolymer comprising fromabout 60 to about 80 weight percent propylene, based on the copolymer,and from about 20 to about 40 weight percent olefin comonomer unitshaving 2 to 10 carbon atoms, based on the copolymer, wherein saidpropylene copolymer has a Brookfield Thermosel viscosity of about 1 toabout 2,000 mPa•s at 190° C. and a needle penetration of greater thanabout 150 to about 300 dmm, determined according to ASTM at 23° C. Novelfilms are produced from the novel compositions.

DETAILED DESCRIPTION OF THE INVENTION

The applicant has unexpectedly found that, within the viscosity range ofabout 1 to about 2,000 mPa•s at 190° C., a propylene-ethylene copolymer,having a needle penetration hardness of greater than from about 150 toabout 300 dmm, is useful in stretch cling film compositions based onLDPE, LLDPE, or EVA. The composition of the present invention provides ablown stretch cling film having a good balance between maximizing peelcling strength and acceptably low high-speed unwinding noise.

It was surprising to find that the stretch cling film composition of thepresent invention provides a film having excellent peel cling whenstretched to about 200 percent elongation, yet also having good blownfilm properties such as lower haze, higher gloss, and improved puncturepenetration.

The composition of the present invention comprises from about 85 toabout 99 weight percent based on the composition, of an ethyleniccomponent selected from the group of ethylene polymers consisting of lowdensity polyethylene ("LDPE"), linear low density polyethylene("LLDPE"), ethylene vinyl acetate ("EVA"), and mixtures thereof, andabout 1 to about 15 weight percent based on the composition, of apropylene copolymer comprising from about 60 to about 80 weight percentpropylene, based on the copolymer, and from about 20 to about 40 weightpercent based on the copolymers, of olefin comonomer units having 2 to10 carbon atoms. The propylene copolymer has a Brookfield Thermoselviscosity of about 1 to about 2,000 mPa•s at 190° C., and a needlepenetration of greater than about 150 to about 300 dmm, at 23° C.

The ethylene containing polymeric component is a homopolymer of ethyleneor a copolymer of ethylene with a comonomer copolymerizable therewith.More particularly, the ethylene containing polymeric component isselected from a homopolymer of ethylene, an ethylene alpha olefincopolymer, an ethylene vinyl acetate copolymer, and mixtures thereof,wherein the ethylene containing polymeric component has a density nogreater than 0.94 g/cc. The ethylene containing polymeric componentpreferably has a density of from about 0.88 to about 0.93 g/cc, and morepreferably from about 0.89 to about 0.92 g/cc.

The alpha olefin comonomer of the ethylene alpha olefin copolymerpreferably has from 3 to 20 carbon atoms per molecule and is present inan amount of from about 2 to about 20 weight percent based on theethylene alpha olefin copolymer. Examples of the alpha olefin comonomerinclude 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene,1-nonene, 1-decene, 1-dodecene, a terpolymer of ethylene, a terpolymerof 1-butene, a terpolymer of 1-hexene, and mixtures and derivativesthereof. In a preferred embodiment, the alpha olefin is selected from1-butene, 1-hexene and 1-octene.

The ethylene containing polymeric component may be prepared readily byany conventional technique known in the art.

Stretch wrap film made from blown film processes is generally strongerthan film made from casting. Since LDPE and EVA are not as strong asLLDPE films, the preferred ethylenic component of the present inventionis LLDPE. LLDPE has excellent machine direction (MD) elongation, goodtear resistance, good tensile strength, and good puncture resistance.LLDPE is a copolymer of ethylene and an alpha olefin, with density offrom about 0.88 to about 0.94 g/cm³ and a melt index of about 0.4 to 8g/10 min. The LLDPE used is more preferably an ethylene-octene orethylene-hexene LLDPE copolymer. The presence of up to about 20 weightpercent LDPE, along with the LLDPE, improves processability, bubblestability, and optical properties.

The ethylenic containing polymeric component comprises from about 85 toabout 99 weight percent of the present composition and the propylenecopolymer comprises from about 1 to about 15 weight percent of thecomposition. More preferably, the composition comprises about 90 toabout 99 weight percent ethylenic polymer, and from about 1 to about 10weight percent propylene polymer, based on the composition.

The novel propylene copolymers, of the present invention are very lowmolecular weight copolymers, comprising from about 60 to about 80percent by weight propylene, based on the copolymer, and from about 20to about 40 weight percent based on the copolymer, of C2 to C10 alphaolefin comonomer unit content. The propylene copolymer preferably hasabout 20 to about 35 weight percent olefin comonomer unit content andfrom about 65 to about 80 weight percent propylene. Copolymerscomprising from about 70 to about 80 weight percent propylene and about20 to about 30 weight percent olefin comonomer units are more preferred.The alpha olefin comonomer units are preferably ethylene units.

The molecular weight of the propylene copolymer of the present inventionis critical. The low molecular weight is evidenced by the viscosityvalues at 190° C., determined by the Brookfield Thermosel melt viscositymethod. This very low viscosity range of the propylene copolymer is fromabout 1 to about 2,000 mPa•s, at 190° C. The viscosity is preferablyfrom about 1 to about 1,500 mPa•s at 190° C., with about 1 to about 800mPa•s at 190° C. being more preferred.

The propylene copolymer of the present invention has a needlepenetration of greater than about 150 to about 300 dmm, determined byASTM (test method modified to 23° C., instead of 25° C.). The propylenecopolymer preferably has a needle penetration of about 175 to about 300dmm at 23° C., with about 200 to about 300 dmm at 23° C. being morepreferable.

The propylene copolymer component of the composition utilized herein maybe produced by a process disclosed in Canadian Patent 1,296,484,entitled "Process for the Direct Synthesis of Highly Amorphous PropyleneHomopolymers and Propylene--Ethylene Copolymers." The contents ofCanadian Patent 1,296,484 are incorporated herein by reference.

The exact amounts of the ethylene containing polymeric component and thepropylene polymer component of the compositions herein are determined bythe application for which film produced therefrom is to be employed.Variation of the amounts of each component is within the scope of oneskilled in the art.

For many purposes, it may be desirable to incorporate other conventionaladditives with the compositions of the present invention. For example,there may be added antioxidants, heat and light stabilizers, dyes,antistatic agents, preservatives, processing aids, pigments, flameretardants, and the like.

The compositions of the ethylene containing polymeric component definedhereinabove and the propylene polymer defined hereinabove are readilyprepared by any method known in the art. For example, the components ofthe composition may be blended together by melt extrusion or may beadmixed together on a conventional mixing machine such as an extruder ora continuous mixer.

The composition of the present invention has a good peel cling strengthfor use in forming stretch wrap film. It is now commonplace for stretchwrap film to be elongated to 200 percent and higher, during a stretchwrapping process. Peel cling strength generally decreases with moreelongation. Therefore, it is important to determine that the peel clingstrength of a film be adequate when elongated, instead of being measuredonly when unstretched, as has been past practice. At 200 percentelongation, film produced from the composition of the present inventionpreferably has a peel cling strength of about 100 to about 500 g/2.54cm, preferably about 100 to about 400 g/2.54 cm, with about 100 to about300 g/2.54 cm being still more preferable, determined using ASTM MethodD5458-95 "Standard Test Method for Peel Cling of Stretch Wrap Film".

The composition of the present invention can be formed into stretch wrapfilm using any technique known in the art such as a cast method or blownfilm method. The present invention includes a blown film process whereinan extruder having an annular die is used for extruding the compositionof the present invention. Air is blown in through the extruder die toform a bubble of the present polymer blend having a blow-up ratio of 1to 3.5 times the die diameter. After a cooling air stream cures thefilm, the film is wound onto rolls. More particularly, a composition asdefined hereinabove is introduced into the feed hopper of an extruderthat is water-cooled and resistance heated. The films were producedusing an annular die having a die gap of about 2.24 mm having a dualorifice nonrotating, nonadjustable air ring. The film is extrudedthrough the die into a film that is cooled by blowing air onto thesurface of the film in a blowing manner. The film is drawn from the dietypically forming a cylindrical film that is cooled, collapsed,optionally slit, and wound to form a roll of film. In preparing castfilm, any of the well known cast film forming procedures may beutilized.

The present invention further includes a film of the composition of thepresent invention. The preferable film is a blown stretch wrap clingfilm. The film generally has a higher impact strength and a higher glossthan the neat LLDPE. The film made from the composition of the presentinvention generally also has a high speed unwinding noise not greaterthan the unwinding noise of neat LLDPE. This is important in light ofthe OSHA noise workplace restrictions. The present invention alsoincludes articles of manufacture comprising a film of the composition ofthe present invention. Such articles include monolayer films andmultilayer films in which the film of the composition of the presentinvention is at least one layer.

The present invention further includes a process for stretch wrapping,using a film of the composition of the present invention. The processcomprises wrapping the film of the present invention about the girth ofa unitized plurality of goods so that the film is in a stretchedcondition and the end region of the film is attached to a previous areaof film by cling force.

The invention will be more readily understood by reference to thefollowing examples. There are, of course, many other forms of theinvention which will become obvious to one skilled in the art, once theinvention has been fully disclosed, and it will accordingly berecognized that these examples are given for the purpose of illustrationonly, and are not to be construed as limiting the scope of thisinvention in any way.

EXAMPLES

The following test procedures were used in evaluating the analyticalproperties of the compositions herein and in evaluating the physicalproperties of the films of the examples.

Cling values were obtained in accordance with ASTM D5458-95 entitled"Standard Test Method for Peel Cling of Stretch Wrap Film."

Viscosity--ASTM D3236 (at 190° C.)

Needle Penetration--ASTM (at 23° C.)

Melt index--ASTM D1238 (at 190° C.)

Density--ASTM D4888

Example 1

The present example illustrates the usefulness of a propylene-ethylenecopolymer of the present invention in producing an LLDPE film ascompared to a film produced from LLDPE and a propylene-ethylenecopolymer having a needle penetration not within the present invention.The needle penetration data for the propylene-ethylene copolymers shownin Table 1 was determined by ASTM at 23° C.

The propylene-ethylene copolymers in Table 1 were compounded into a 0.9g/10 min. melt index, 0.920 g/cm³ density ethylene-hexene copolymer at alevel of 4% by weight and made into 0.0008 inch (0.020 mm) thick blownfilm. The films were made with a blow-up ratio of about 2.4:1 at about100 feet/minute (30.5 m/minute).

Peel cling properties were measured in accordance with ASTM MethodD5458-95 "Standard Test Method for Peel Cling of Stretch Wrap Film".Peel cling values were measured on both unstretched film and at about200% elongation. The elongated peel cling values more accuratelyrepresent the conditions encountered during pallet wrapping, where thefilm is stretched by pre-stretch rollers or by the pallet load itself.Peel cling values listed in Table 2 were measured 2 weeks after the filmwas produced.

                  TABLE 1                                                         ______________________________________                                        Properties of Propylene-Ethylene Copolymers                                   Propylene  Visc., mPa · s at                                                                            Needle Pen.                                Copolymer  190° C.                                                                            Wt. % Ethylene                                                                            dmm                                        ______________________________________                                        A (Comparison)                                                                           235         15.9        109                                        B          275         25.7        263                                        C          158          21.46      242                                        ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Peel Cling of Blown LLDPE Films Containing 4% Propylene-Ethylene              Copolymer                                                                     Propylene Copolymer                                                                        Unelongated Peel                                                                           Elongated Peel Cling,                               in Film      Cling, g/2.54 cm                                                                           g/2.54 cm                                           ______________________________________                                        None          0            0                                                  A (Comparison)                                                                             296          186                                                 B            321          187                                                 C            298          214                                                 ______________________________________                                    

The data in Table 2 indicates that blown films produced from LLDPE andpropylene-ethylene copolymers of the present invention (Sample B and C)showed equal or higher peel cling than a comparative film produced fromLLDPE and a propylene-ethylene copolymer (Sample A) not within thepresent invention, which is commercially utilized in such films.

It should be clearly understood that the forms of the invention hereindescribed are illustrative only and are not intended to limit the scopeof the invention. The present invention includes all modificationsfalling within the scope of the following claims.

What is claimed is:
 1. A composition comprising:(a) from about 85 toabout 99 weight percent, based on the total weight of the composition,of a component selected from the group consisting of a homopolymer ofethylene, an ethylene alpha olefin copolymer, an ethylene vinyl acetatecopolymer, and mixtures thereof, wherein the component has a density nogreater than 0.94 g/cc; and (b) from about 1 to about 15 weight percent,based on the total weight of the composition, of a propylene copolymercomprising about 20 to about 40 weight percent based on the copolymer ofolefin comonomer units having 2 to 10 carbon atoms and from about 60 toabout 80 weight percent propylene, based on the copolymer, wherein thepropylene copolymer has a Brookfield Thermosel viscosity of about 200mPa•s at 190° C. and a needle penetration of greater than about 150 toabout 300 dmm, determined according to ASTM at 23° C.
 2. The compositionaccording to claim 1 wherein the component has a density of from about0.88 to about 0.93 g/cc.
 3. The composition according to claim 1 whereinthe component is an ethylene alpha olefin copolymer wherein the alphaolefin comonomer has from 3 to 20 carbon atoms and is present in anamount of from about 2 to about 20 weight percent based on the ethylenealpha olefin copolymer.
 4. The composition according to claim 3 whereinthe alpha olefin comonomer is selcted from 1-butene, 1-hexene and1-octene.
 5. The composition according to claim 1 wherein the olefincomonomer units of the propylene copolymer are ethylene units.
 6. Thecomposition according to claim 1 wherein the propylene copolymercomprises from about 20 to about 35 weight percent olefin comonomerunits, and from about 65 to about 80 weight percent propylene.
 7. Thecomposition according to claim 6 wherein the propylene copolymercomprises from about 20 to about 30 weight percent olefin comonomerunits, and from about 70 to about 80 weight percent propylene.
 8. Thecomposition according to claim 1 wherein the propylene copolymer has aBrookfield Thermosel viscosity of from about 1 to about 1500 mPa•s at190° C.
 9. The composition according to claim 8 wherein the propylenecopolymer has a Brookfield Thermosel viscosity of from about 1 to about800 mPa•s at 190° C.
 10. The composition according to claim 1 whereinthe propylene copolymer has a needle penetration of about 175 to about300 dmm at 23° C.
 11. The composition according to claim 10 wherein thepropylene copolymer has a needle penetration of about 200 to about 300dmm at 23° C.
 12. The composition according to claim 1 wherein thecomponent is present in an amount of about 90 to about 99 weight percentand the propylene copolymer is present in an amount of about 1 to about10 weight percent.